1. Field of the Invention
The present invention relates to a display device. More particularly, the present invention relates to a display device of a DLP (Digital Lighting Processing) system where drive current which is controlled in a linear mode is supplied to a light source.
2. Description of the Related Art
In current display devices, light sources for improved color reproduction are changed from systems using conventional CCFLs (Cold Cathode Fluorescent Lamps) to systems using LEDs (Light Emitting Diodes). As described above, the display device with a light source using LEDs enhances color reproduction performance.
In the case of a DLP system, an image is divided into several sheets of bit-planes with respectively different lengths in time. The divided sheets of the bit-planes are sequentially displayed on a screen. Accordingly, in a display device comprising a DLP system, the intensity of light corresponding to each bit-plane should be uniform. When the intensity of light corresponding to each bit-plane is not uniform, linearity in a gradation of an image displayed on a DLP display device becomes bad, or a gradation becomes unstable. Accordingly, in order to use LEDs as a light source in a DLP display device, current flowing through LEDs should be precisely controlled so that noise such as switching pulsation is suppressed. As a bit-plane is varied, a current value required for current flowing through LEDs is varied. Since a transient section where the current value is varied is not used for a display on a screen, a current control circuit comprising a fast response speed is required.
A current source circuit of a linear regulator type is used to provide electric power with a fast response speed and having no noise for a display device. That is, it is preferable that electric power is provided in a linear mode. However, in the case of a linear mode, a switching unit used for regulating voltage may be unable to control current flowing through LEDs when the characteristics of LEDs or the number of LEDs are altered or when the dispersion of LEDs is changed. Supplying sufficient power for the switching unit after considering all variable factors of LEDs may produce problems such as heat generation of an electric power supply circuit, reduce an efficiency of the electric power supply circuit, and make it difficult to control the electric power supply circuit.
IF a short-circuited and open-circuited status of LEDs is not well detected, the LEDs may not be controlled properly. For example, in the case of the short-circuited LEDs, the switching unit is overheated which may result in a fire.
Accordingly, there is a need for an improved display device capable of supplying a stable electric power for a light source.